The overall objective of this effort is to create a comprehensive package of free software tools for computer simulations of ultrasonic and electromagnetic modalities for therapy and imaging applications. In particular, the software developed within this effort will significantly reduce the computation time required for large ultrasound phased array simulations without increasing the numerical error. These fast ultrasound simulations will reduce the computation time by a factor of four or more for most applications, which is especially important for parametric studies that run for days or weeks on modern desktop computers. The software created will also reduce the software development time required for simulations of biomedical ultrasonic and electromagnetic systems, thereby eliminating duplicated software development efforts by establishing a common framework for the evaluation of therapy and imaging strategies. The specific aims for the R21 phase of this effort are: 1. develop a suite of routines for fast simulations of ultrasound devices and arrays designed for therapeutic applications; 2. create a simulation package that performs fast simulations of ultrasound arrays for diagnostic imaging; and 3. construct interfaces and simulation routines for finite element (FE) and finite difference time domain (FDTD) modeling of electromagnetic (EM) systems designed for thermal therapy and targeted drug delivery. The R33 phase will extend the results of the R21 by a) deriving fast methods for simulating pressure fields produced by curved strip transducers, b) creating new simulation approaches that further reduce the computation times by exploiting redundancies in large array simulations, c) developing new simulation software for nonlinear ultrasound propagation, and d) constructing convenient interface tools and simulation routines for the electromagnetic component of hybrid systems designed for therapy and imaging. In each phase of this effort, simulation routines will be developed, validated, and documented, examples will be provided for simulations of therapy and imaging, and then the software will be distributed through a web portal. The resulting comprehensive software package, which will include a convenient user interface, will facilitate rapid evaluation of ultrasonic and electromagnetic array systems for therapy and imaging research. [unreadable] [unreadable] [unreadable]